by Grant Allen
Simultaneously with this change from fertilisation by the wind to fertilisation by insects, there came in another improvement in the mechanism of flowers. Probably the primitive blossom consisted only of stamens and pistil, with, at best, a single little scale or leaf as a protection to each. But some of the five-rowed flowers now began to change the five stamens of the outer row into petals; that is to say, to produce broad, bright-coloured, and papery flower-rays in the place of these external stamens. The reason why they did so was to attract the insects by their brilliant hues; or, to put it more correctly, those flowers which happened to display brilliant hues as a matter of fact attracted the insects best, and so got fertilised oftener than their neighbours. This tendency on the part of stamens to grow into petals is always very marked, and by taking advantage of it gardeners are enabled to produce what we call double flowers; that is to say, flowers in which all the stamens have been thus broadened and flattened into ornamental rays. Even amongst wild flowers, the white water-lily shows us every gradation between fertile pollen-bearing true stamens and barren broad-bladed petals. To put it shortly and dogmatically, petals are in every case merely specialised stamens, which have given up their original function of forming pollen, in order to adopt the function of attracting insects.
Fig. 8. — Transition from stamen to petal in White Water-lily.
The five-rowed ancestors of the daisy found a decided advantage in thus setting apart one outer row of stamens as coloured advertisements to lure the insects to the honey, while they left the inner rows to do all the real work of pollen-making. They very rapidly spread over the world, and assumed very various forms in various places. But wherever they went, they always preserved more or less trace of their quinary arrangement; and to this day, if you pick almost any flower belonging to the same great division of dicotyledons (the name is quite unimportant), you will find that it has at least some trace of its original arrangement in rows of five. The common stonecrop and its allies keep up the arrangement best of any; for they have each, as a rule, five petals; each petal has its separate bract, making a calyx or flower-cup of five pieces or sepals; inside are one or two rows of five stamens each; and in the centre, a pistil of five carpels. Such complete and original symmetry as this is not now common; but almost all the five-rowed flowers retain the same general character in a somewhat less degree. The buttercup, for example, has one outer row of five sepals, then five petals, and then several crowded rows of stamens and carpels. And in the petals at least the harmony is generally complete. There are five in the dog-rose, in the violet, in the pea-blossom, in the pink, in the geranium, and (speaking generally) in almost every plant that grows in our gardens, our fields, or our woodlands, unless it belongs to the other great division of trinary flowers, with all their organs in groups of three. And now, if you will pull open one of the inner yellow florets of your daisy, you will see that it has five stamens and five little lobes to the bell-shaped corolla, to show its ancestry plainly on its face, and ‘to witness if I lie.’
Fig. 9. — Corolla of Primrose.
Fig. 10. — Corolla of Harebell.
But the original bright-coloured ancestor of the daisy must have had five separate petals, like the dog-rose or the apple-blossom at the present day. How then did these petals grow together into a single bell-shaped corolla, as we see them now in the finished daisy? Well, the stages and the reasons are not difficult to guess. As flowers and insects went on developing side by side, certain flowers learnt to adapt themselves better and better to their special insects, while the insects in return learnt to adapt themselves better and better to their special flowers. As bees and butterflies got a longer proboscis with which to dive after honey into the recesses of the blossoms, the blossoms on their part got a deeper tube in which to hide their honey from all but the proper insects. Sometimes this is done, as in the larkspur, the violet, and the garden nasturtium, by putting the honey at the bottom of a long spur or blind sac; and if you bite off the end of the sac in the nasturtium you will find a very appreciable quantity of nectar stored up in it. But most highly specialised flowers have hit upon a simpler plan, which is to run all their petals together at the bottom into a tube, so long that no useless insect can rob the honey without fertilising the plant, and so arranged that the proboscis of the bee or butterfly can rub against the stamens and pistil on the way down. In pinks and their allies we see some rude approach to this mode of growth; for there each petal has a long claw (as it is called), bearing the expanded part at the end; and these claws when firmly pressed together by the calyx practically form a tube in five pieces: but in the perfectly tubular flowers, like the primrose, the arrangement is carried a great deal further; for there we have the claws all grown into a single piece, with the expanded petals forming a continuous fringe of five deeply cleft lobes, representing the five original and separate pieces of the pinks. Now, in the primrose, again, we still find the five petals quite distinct at the edge, though their lower portion has grown together into a regular tube; but in the harebell or the Canterbury bell we see that the whole blossom has become bell-shaped, and that the five originally separate petals are only indicated by five slightly projecting points or lobes which give the tubular corolla its vandyked margin. And if you look at the little central florets of the daisy or the sunflower, you will observe that they too exactly resemble the Canterbury bell in this particular. Hence we can see that their ancestors, after passing through stages more or less analogous to those of the pinks and the primroses, at last reached a completely united and tubular or campanulate form, like that of the heath or the Canterbury bell.
Fig. 11.
Section of floret of Daisy.
There is one minor point, however, in the development of the daisy which I only notice because I am so afraid of that terrible person, the microscopic critic. This very learned and tedious being goes about the world proclaiming to everybody that you don’t know something because you don’t happen to mention it; and for fear of him one is often obliged to trouble one’s readers with petty matters of detail which really make no difference at all except to such Smelfunguses in person. Being themselves accustomed to weary us with the whole flood of their own unspeakable erudition, every time they open their mouths, they imagine that everybody else must be ignorant of anything which he doesn’t expressly state; as though you might never talk of a railway journey without giving at full the theory of kinetic energy as applied to the coal in the furnace. For their sake, then, I must add that, when the daisy’s ancestors had reached a level of development equivalent to that of the heath and the Canterbury bell, they differed in one respect from them just as the primrose still does. In the heath and the harebell, the stamens remain quite separate from the tube formed by the petals; but in the primrose and the daisy the stalks of the stamens (filaments, the technical botanists call them) have coalesced with the petals, so that the pollen seems to hang out in little bags from the walls of the tube itself. This is a further advance in the direction of specialised arrangements for insect-fertilisation; and it shows very simply the sort of cross-connections which we often get among plants or animals. For while the daisy is more like the Canterbury bell in the shape of its corolla, it is more like the primrose in the arrangement of its stamens. Or, to put it more plainly, while the Canterbury bell has hit upon one mode of adaptation in the form of its tube, and while the primrose has hit upon another mode in the insertion of its stamens, the daisy has hit upon both together, and has combined them in a single flower. And now, my dear Smelfungus, having given way to your prejudices upon this matter, allow me to assure you that nothing will induce me to enter into the further and wholly immaterial difference between hypogynous and epigynous corollas. For every one but you, the very names, I am sure, will be quite sufficient apology for my reticence. These, in fact, are subjects which, like the ‘old familiar Decline and Fall off the Rooshian Empire,’ had better be discussed ‘in the absence of Mrs. Boffin.’
When the ancestors of the
daisy had reached the stage of united tubular blossoms, like the harebell, with stamens fastened to the inside wall of the tube, like the primrose, they must, on the whole, have resembled in shape the flowers of the common wild white comfrey, more nearly than any other familiar English plant. The next step was to crowd a lot of these bell-shaped blossoms together into a compact head. If you compare a cowslip with a primrose, you can easily understand how this is done. According to many of our modern botanists, cowslips and primroses are only slightly divergent varieties of a single species; and in any case they are very closely related to one another. But in the primrose the separate blossoms spring each on a long stalk of its own from near the root; while in the cowslip, the common stem from which they all spring is raised high above the ground, and the minor flower-stalks are much shortened. Thus, instead of a bunch of distinct flowers, you get a loose head of crowded flowers. Increase their number, shorten their stalks a little more, and pack them closely side by side, and you would have a compound or composite flower like the daisy. In fact, we often find in nature almost every intermediate stage: for instance, among the pea tribe we have all but solitary flowers in the peas and beans, long clusters in the laburnum and wistaria, and compact heads in the clovers. The daisies and other composites, it is true, carry this crowding of flowers somewhat further than almost any other plants; but still even here you can trace a gradual progress, some approach to their habit being made by allied families elsewhere; while some composites, on the other hand, have stopped short of the pitch of development attained by most of their race. Thus, certain campanulas have their flowers packed tightly together into a head, which looks at first sight a single blossom, just as deceptively as the daisy does; and a still nearer relative, the scabious, even more strikingly resembles the composite form. So that the daisies and their allies have really only carried out one step further a system of crowding which had been already begun by many other plants.
Fig. 12. — Section of head of Daisy.
If you look closely at the daisy, you will see in what this crowding consists. The common flower-stalk is flattened out at the end into a regular disk, and on this disk all the florets are seated with no appreciable separate flower-stalks of their own. Outside them a double row of leaves is arranged, exactly like the calyx in single flowers, and serving the same protective purpose — to preserve the florets from the incursions of unfriendly insects; while inside, the little individual blossoms have almost lost their own calyxes which are scarcely represented by a few tiny protuberances upon the seed-like fruit. In the daisy, indeed, we may say that the true calyx has been dwarfed away to nothing; but in the dandelion and many other composites a new use has been found for it; it has been turned into those light feathery hairs which children call ‘the clock,’ and which aid the dispersion of the seeds by wafting them about before the wind.
Now, what has made the daisy and the other composites grow so small and thick-set? Probably the need for attracting insects. By thus combining their mass of bloom they are enabled to make a great show in the world, and to secure the fertilisation of a great many flowers at once by each insect which visits the head. For each floret has its own little store of honey, its own stamens, and its own pistil containing an embryo fruit; and when a bee lights upon a daisy head, he turns round and round, extracting all he can get from every tiny tube, and so fertilising the whole number of florets at a single time. The result at least proves that the principle is a good one; for few flowers get so universally fertilised, or set their seed so regularly, as the composites. Though they must have reached their present very high state of evolution at a comparatively recent period, they have spread already over the whole world; and they are far more numerous, both in individuals, in species, and in genera, than any other family of flowering plants. In fact, they are undoubtedly the dominant tribe of the whole vegetable kingdom. When I say that in Britain alone they number no less than 120 species, including such common and universal weeds as the daisy, dandelion, thistles, groundsel, camomile, milfoil, hawkweed, and burdock, it will be clear that nine out of every ten ordinary wayside blossoms which we see on any country walk are members of this highly evolved, ubiquitous, and extremely successful family.
Still, we are far from having finished the pedigree of the daisy. We have traced its general genealogy down as far as the common composite stock: we have now to trace its special derivation from the early common composite type to the distinctive daisy form. Clearly one great point in the daisy’s history is yet untouched upon; and that is the nature and meaning of the white rays. We know that the inner yellow florets are (as it were) dwarfed and specialised golden harebells; but we do not yet know what is the origin of these long outer streamers, which look so wholly unlike the tiny and regular central bells.
In solving this problem, the other composites will help us not a little; for we must always seek in the simpler for the interpretation of the more complex; and the daisy, instead of being the simplest, is one of the most developed representatives of the composite pattern. If you turn to that tall, rank-looking weed growing yonder, under cover of the hedge, you will get a good surviving example of the earliest form of composite. The weed is a eupatory— ‘hemp agrimony’ the country people call it — and it has small heads, each containing a few tubular purple florets, all exactly the same size and shape, and all much more loosely gathered together than in the daisy or the dandelion. The eupatory is interesting as preserving for us one of the first stages in the ancestry of the higher composites, after they had attained to their distinctive family characteristics. Once more, I don’t wish you to understand that the daisies are descended from the eupatory: all I mean is, that their ancestors must once have passed through an analogous stage; and that the eupatory has never got beyond it, while the daisies have gone on still further differentiating and adapting themselves till they reached their present peculiar form. Now, if you compare this daisy with the head of eupatory, you will see that they differ in two particulars — the daisy has outer rays, while the eupatory has none; and the inner daisy florets are yellow, while the eupatory florets are purple. The latter difference is one into which we cannot enter now: it must suffice to say that when the daisy’s ancestors were in the eupatory stage of development they had apparently all their florets yellow. This is likely, because almost all the modern composites of every sort have yellow central florets, and most of them have yellow rays as well. It is only a few kinds that have red or purple central florets; and, as we shall soon see, only a few also that have white or pink outer rays.
What, then, made the daisy’s ancestors produce a row of external florets so different in shape and colour from the internal ones? The answer is exactly analogous to that which I have already given for the origin of petals themselves. Compare the eupatory with the daisy once more, and you will see that the one is comparatively inconspicuous, while the other is very noticeable and bright-coloured. The row of green bracts almost hides the blossoms of the eupatory; but the large white rays make a bold and effective advertisement for the daisy. Certain composites, in fact, have just repeated the same device by which the earliest petal-bearing flowers sought to attract the notice of insects. Those early flowers, as we saw, set apart one outer row of stamens as bright-coloured petals; these later compound flower-heads have set apart one outer row of florets as bright-coloured rays. If you examine the rays closely, you will see that each of them is a separate little flower, with the stamens suppressed, and with the bell-shaped corolla flattened out into a long and narrow ribbon. Even these very abnormal corollas, however, still retain a last trace of the five original distinct petals; for their edge is slightly notched with five extremely minute lobes, often nearly obliterated, but sometimes quite marked, and almost always more or less noticeable on a careful examination. A daisy thus consists of a whole head of tiny tubular bells, the inner ones normal and regular, with corolla, stamens, and pistil, and the outer ones flattened or ligulate, with the stamens wanting, and the entire floret
simply devoted to increasing the attractiveness of the compound mass. Pull off the rays, and you will see at once what an inconspicuous flower the daisy would be without them.
Last of all, the question arises, Why are the outer florets or rays pink and white, while the inner florets or bells are golden yellow? When we have solved that solitary remaining problem, we shall have settled the chief points in the daisy’s pedigree. Clearly, when the rays were first produced, they must have been yellow like the central florets. The mere flattening and lengthening of the corolla would not in itself tend to alter the colour. And as a matter of fact, the vast mass of those composites which have progressed to the stage of having rays — which have got these two separate forms of flowers, for show and for use respectively — have the rays of the same colour as the central bells, that is to say, generally yellow. Of this stage the sunflower is a familiar and very striking representative. It has bright golden central florets, and large expanded rays of the same colour. To anybody who wants to study the structure of the daisy without a microscope, the sunflower is quite as valuable and indispensable as it is to our most advanced æsthetic school in painting and decoration. Moreover, it shows us admirably this intermediate stage, when the compound flower-head has acquired a distinct row of outer attractive florets, adding wealth and expansiveness to its display of colour, but when it has not yet attempted any specialisation of hue in these purely ornamental organs. The daisy, however, together with the camomile, the ox-eye daisy, and many other similar composites, has carried the process one step further. It has coloured its rays white, and has even begun to tinge them with pink. This makes these highest of all composites the most successful plants in the whole world. If one considers that daisies begin to bloom on January 1, and go on flowering till December 31; that they occur in almost every field far more abundantly than any other blossom; and that each one of them is not a single flower, but a whole head of flowers — it will be quite clear that they are much more numerous than any rival species. And when we add to them the other very common white-rayed composites, such as the camomiles, many of which abound almost as freely in their own haunts and at their proper season, it is obvious that this highly evolved composite type is the dominant plant race of the old world at least. In the new world, their place is taken by a somewhat more developed type still, that of the Michaelmas daisies, which have their rays even more ornamental than our own, and brightly coloured with mauve or lilac pigment. All the world over, however, in and out of the tropics, the commonest, most numerous, and most successful of plants are ray-bearing composites of one kind or another, like the daisies, with the rays differing in colour from the central florets.
